2 2 types of weathering Mechanical Weathering Occurs when physical forces break rock into smaller & smaller pieces without changing the rock’s mineral compositionChemical WeatheringThe transformation of rock into 1 or more new compounds
3 Mechanical Weathering Breaking a rock into smaller pieces increases the total surface areamore SA is exposed to chemical weatheringUnloadingExfoliation (layers of onion)Causes the outer layers of the rock to expand more than the rock belowIgneous rock may be exposed by uplift & erosion of overlying rocks. Pressure exerted on the igneous rock is reduced.Frost WedgingWater freezes and expandsFrozen water in rocks expand cracksFreeze – thaw cycles = rock breaks into pieces
4 Chemical Weathering Water Most important factor in CW Absorbs gases in the atmosphere & groundChemical Weathering of GraniteCan change the properties of rocksChemical Weathering of Silicate MineralsMake up most of Earth’s crustNa, Ca, K, Mg they contain dissolve & are carried away by groundwaterSpheroidal WeatheringForm of CWCorners & edges become more rounded by CW
5 Rate of Weathering Differential Weathering Different parts of rock mass often weather at different ratesFactors that affect the rate of chemical weathering:Rock CharacteristicsClimateTemperature, MoistureHigh Temps. & high moisture are best for chemical weatheringMechanical WeatheringBy breaking rock into small pieces MW accelerates CW by increasing the SA
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